The stiffness of a blood vessel in a living thing, particularly, a human being, can be used in assessing the health of the blood vessel. Presently, there are at least two known techniques for estimating vessel stiffness.
One technique involves assessing vessel stiffness by measuring the internal pressure within a vessel and dimensional changes resulting from pressure changes. However, it is very difficult to measure internal pressure within a vessel inside a body, and moreover, systems and apparatus to make external pressure measurements are not easily calibrated and require compressing the vessel.
Another technique for estimating vessel stiffness entails measuring a pressure propagation velocity. The pressure propagation velocity is a measure that is known to be very closely correlated with vessel stiffness and is a measure of the velocity with which a pressure pulse propagates along a vessel.
Both of the foregoing techniques require one or more pressure measurements of some sort that is very difficult to implement in vivo. To make these measurements, pressure transducers are placed externally on the body, e.g., on the skin of a person's body, and are monitored by an appropriate monitoring system in order to estimate pressure changes in vessels under the skin. There are many corrupting influences and limitations of this procedure. Because the pressure transducers are usually placed a large distance apart, for example, a half of a meter in some cases, local regions of vessels cannot be effectively isolated and analyzed for, for example, plaque formation, thrombi (blood clots), aneurysms, etc. Furthermore, when pressure transducers are used externally on a body, only vessels near the surface of the body can be analyzed. In other words, internal vessels, such as the important abdominal aorta associated with the heart, which degrades in most elderly people, cannot be analyzed.
Thus, a heretofore unaddressed need exists in the industry for a way to better quantitatively measure vessel stiffness, to thereby assess vessel health in a living thing.